The present invention relates to a guide roller for guiding a magnetic tape in the magnetic tape cassette and a method of manufacturing the same.
Conventionally, a magnetic tape cassette is widely used as a storage medium. The magnetic tape cassette is divided into ones for consumer use and ones for industrial use depending on the purpose. FIG. 20 is an exploded perspective view showing main components of a BETACAM L cassette that is a magnetic tape cassette for commercial use.
As shown in FIG. 20, the BETACAM L cassette (hereinafter referred to as “magnetic tape cassette”) 20 generally comprises an upper cassette half and a lower cassette half 22 constituting a cassette case, a pair of tape reels which is rotatably received in the upper and lower cassette halves 24, 22 and on which a magnetic tape 26 is wound, and a lid 32 for opening and closing the opening formed on the front end side of the upper and lower cassette halves 24 and 22.
On the lower cassette half 22, guide rollers 36 and metallic guide pins 38 are mounted at both sides of the opening on the front end side across which a magnetic tape 26 is to be routed. In addition, pads 44 to be in sliding contact with the back side of the magnetic tape 26 is mounted on the lower cassette half 22. On the upper cassette half 24, there are provided reel springs 28 for urging the respective tape reels 28, 30 via the reel holders 46, and center caps 50 for engaging the reel springs 48 from outside of said cassette half 24. The upper and lower cassette halves 24, 22 are fixed together by a plurality of screws 34.
Among components described above, the guide roller 36 is a cylindrical member formed of a smooth and mechanically strong resin such as POM, and rotatably supported on the lower cassette half 22 by being loosely fitted on the trunnion pin 36A fixed on the lower cassette half 22.
FIG. 21 is an enlarged view of the guide roller 36 and the guide pin 38 on the lower cassette half 22 viewed in the direction shown by the arrow B in FIG. 20. In FIG. 21, there is shown a state where the magnetic tape 26 is routed from the tape reel 28 (See FIG. 20) over the guide roller 36 and the guide pin 38. The pad 44 is in sliding contact with the back surface of the magnetic tape 26 between the tape reel 28 and the guide roller 36 and urges the magnetic tape 26. As a consequent, the magnetic tape 26 comes into contact with the outer periphery of the guide roller 36. When the magnetic tape cassette 20 is loaded on the recording/replaying apparatus, not shown, and replayed or rewound, the magnetic tape 26 is passed on the outer periphery of the guide roller and then routed out from the cassette case and then travels over the magnetic head of the recording/replaying apparatus.
FIG. 22 is a cross sectional view taken along the line C—C in FIG. 21. The guide roller 36 is cylindrical in shape and the outer periphery thereof has a uniform diameter.
In the guide roller 36 of the magnetic tape cassette 20 as described above, there are cases where the magnetic tape 26 being in contact with the guide roller 36 is displaced from the normal position upwardly along the axis of said guide roller or downwardly along the same though it is not shown, and thus the magnetic tape 26 does not travel stably. As a consequent, when the magnetic tape 26 is traveling over the magnetic head of the recording/replaying apparatus, the position of the magnetic tape 26 may be displaced with respect to the magnetic head, and thus reading or writing of the record cannot be accomplished properly. This is a problem.
On the other hand, when molding a guide roller 36 described above by injection molding, the parting line PL of the mold is normally defined along the end surface of the molded object. However, it has been a very troublesome work to take an elongated guide roller out of the mold. Though it is also possible to form the guide roller 36 by cutting a bar by machining, it requires a long process time. In addition, since a costly machine such as NC lathe is required for such a cutting work, the processing cost increases to a significant level.
In order to solve this problem, the parting line of the injection mold may be defined along the center portion or along the axis thereof. However, defining the parting line in this way generates molding burr that projects all along the periphery thereof, and thus the secondary process such as cutting work must be made by a machine for deburring, which results in increase in time and effort. This is also a problem.
In addition, since the guide roller 36 shown in FIG. 22 guides the magnetic tape 26, it is supported with good rotatability, and thus when the magnetic tape 26 travels at high velocity such as fast forwarding operation or fast rewinding operation, the guide roller 36 rotates at high velocity accordingly. Consequently, at least one of the guide roller 36 and the upper and lower cassette halves 24, 22 is cut down by friction between the upper and lower end surfaces of the guide roller 36 and the inner surfaces of the upper and lower cassette halves 24, 22, and resultant cutting powder may be attached on the magnetic tape 26 and cause a dropout.
It has been shown that when the magnetic tape 26 is running at low velocity for replaying the record, the guide roller also rotates at a low velocity and the upper and lower end surfaces of the guide roller 36 comes into contact with the inner surfaces of the upper and lower cassette halves 24, 22, but cutting powder is not generated during low velocity rotation. This is a problem.